Enhanced photoelectrochemical performance of hydrothermally grown tetravalent impurity (Si⁴⁺) doped zinc oxide nanostructures for solar water splitting applications

We report the photoelectrochemical performance of Si-doped ZnO nanorods (NRs) synthesized via two step sol–gel and hydrothermal technique. In the X-ray diffraction patterns the prominent (002) peak confirms the hexagonal wurtzite phase for all samples. In addition to this, the Field Emission Scanning Electron Microscopy images also confirm the hexagonal shape of the NRs with the inclusion of this group IV dopant. The absorption spectra clearly indicates the increase in absorbance in the visible region after doping Si as compared with the undoped ZnO NRs. Bandgap tuning has been noted to be possible after doping. With the insertion of Si⁴⁺ ion into the ZnO matrix, the oxygen defects acting as recombination centers are reduced, as observed from the photoluminescence (PL) spectrum. We obtain a photocurrent density of 1.101 mA cm⁻² values (approximately 4.5 times higher than the ZnO sample) at + 0.438 V in presence of 0.1 M NaOH electrolyte solution under visible light illumination (AM 1.5G) for the 8% Si-doped ZnO NRs sample. We attribute this enhancement to the reduction in recombination centers causing suppression of electron–hole recombination due to the reduced oxygen defects as observed in the PL spectrum. The enhanced absorption along with higher surface area of the NRs also promoted the increase in photocurrent value for this Si doped sample. The stability tests conceived that the doped ZnO NRs samples can better behave as a promising photoelectrode material for further generation of clean green energy.